In a small pot, add lemongrass, grated ginger, sugar and 1/2 cup water.,Bring to a boil and let sugar dissolve. Remove pan from heat and allow to steep and cool for about 30 mins.,Strain the syrup through a fine sieve.,Mix in lemon juice, yeast and 7 cups water. Whisk together.,______,Make sure to refrigerate after it starts to carbonate.